Operating systems cannot be uninstalled like programs such as Microsoft Office and Quickbooks. However if you have a dual boot system that is a different procedure. These instructions are for a single boot system (only one operating system installed). Insert the operating system disk you want to install, XP, Vista, etc…, then restart the computer. Press the delete key to enter the CMOS or BIOS. Change the drive first boot option to CD. Then save and exit. The computer will restart and will begin booting from the CD. It will then prompt there is an operating system installed. You have an option to continue to install the new system or removed the old one first. (1) Select delete partition, then wait for it to finish, (2) Create partition. (3) Format drive using NTS or FAT (FAT is usually faster) After the drive has finished formatting, windows will begin install. You have to agree (F8) then sit back and let it install. Be sure you have all the files you need copied to a disk before you start as this procedure will erase your hard drive completely.